System and process for automatically controlling the flight of power wing airfoils

ABSTRACT

A system ( 1 ) is described for automatically controlling the flight of at least one power wing airfoil ( 2 ), comprising first detecting means ( 3 ) on board of such power wing airfoil ( 2 ) adapted to detect first pieces of information ( 3   a ) dealing with at least one position and one orientation in space of the power wing airfoil ( 2 ) and accelerations to which the power wing airfoil ( 2 ) is subjected; second detecting means ( 5 ) on the ground adapted to detect tension on the driving cables ( 21 ) of the power wing airfoil ( 2 ) and a position of a driving unit ( 9 ) counterweight; processing and controlling means ( 7 ) adapted to transform the contents of such information ( 3   a   , 5   a ) into a mechanical drive operating on the winches of the driving unit ( 9 ) to drive the power wing airfoil ( 2 ) along a flight trajectory TV 1 , TV 2 , TV 3 , . . . , TVn maximising a “lift” effect generated on the power wing airfoil ( 2 ). A process is further described for automatically controlling the flight of at least one power wing airfoil ( 2 ) through the system ( 1 ).

The present invention refers to a system and a process for automaticallycontrolling the flight of power wing airfoils, particularly foroptimising the production of electric energy through the flight of powerwing airfoils connected to a system of the “carousel” type.

As known, there is a wide literature and a relevant number of technicalsolutions related to the automatic control in flight of autonomousaircrafts (UAV). As known, the chance that a person controls the flightof a wing airfoil, such as for example a kite, mainly stems from theevaluation through sight of position and orientation of a wing airfoilin space, which offers the set of perception data which allow modulatingthe manoeuvre of the traction cables. The automation of the manoeuvre ofwing airfoils unavoidably passes through the accurate reproduction ofthis human sensibility.

Reference art and literature however do not show solutions or studieswhich deal with the automatic control of the flight of power wingairfoils, in particular realised as “power kite”. In fact, it is deemedthat problems of this relevant control are multiple and complex, such asto require the most suitable use of the most advanced controlmethodologies and algorithms. The flight of a power wing airfoil and itsmodelisation in fact deal with the use of multi-variable non-linearsystems, with control specifications to be observed with relevantrobustness requirements with respect to parametric variations and todynamics which cannot be modelled with enough accuracy. Depending onsuch characteristics, the control system must also provide controlcalibration functionalities designed on the virtual prototype, usingexperimental measures on the real system, when realised. The problemsposed to the control of real systems by approximations of systemmathematical models used for designing the control, have always beentaken care of by researchers in the field, from the major works ofNyquist and Bode. It is however only starting from the 70's-80's that arelevant development of results occurred, able to systematically andquantitatively deal with the effect of the uncertainty of models usedfor analysing and synthesizing the control systems, giving rise to theenormous development of the robust control area. Since thesemethodologies can be used for solving a great part of real problems, itis necessary that such characterisations are obtained through suitableidentification methods which operate on measures performed on the realsystem to be controlled, designated in reference literature as robustidentification, control-oriented identification or set membershipidentification. Such aspects have been mainly dealt with in thefollowing works:

-   Horowitz, “Synthesis of Feedback Control Systems”, Academic Press,    1963;-   Menga G., Milanese M., Negro A., “Min-max quadratic cost control of    systems described by approximate models”, IEEE Trans. Aut. Contr,    1976;-   J. C. Doyle, “Guaranteed margins for LQG regulators”, IEEE Trans.    Aut. Contr, 1978;-   V. L. Kharitonov, “Asymptotic stability of an equilibrium position    of a family of systems of linear differential equations”,    Differential Equations, 1979;-   G. Zames, “Feedback and optimal sensitivity”, IEEE Trans. Aut.    Contr, 1981-1982;-   H. Kimura, “Robust stabilizability for a class of transfer    functions”, IEEE Trans. Aut. Contr, 1984;-   J. C. Doyle, K. Glover, P. P. Khargonekar, B. A. Francis, “State    space solution to standard H-2 and H-inf control problems”, IEEE    Trans. Aut. Contr, 1989;-   S. P. Bhattacharyya, H. Chapellat, L. H. Keel, “Robust Control: The    Parametric Approach”, Prentice Hall, 1995;-   K. Zhou, J. C. Doyle, K. Glover, “Robust and Optimal Control”,    Prentice Hall, 1996;-   M. Milanese, R. Tempo, A. Vicino (Eds), “Robustness in    Identification and Control”, Plenum, London, 1989;-   IEEE Trans. on Aut. Contr., “Special Issue on System Identification    for Robust Control Design”, 1992;-   A. B. Kurzhanski, V. M. Veliov (Eds), “Modeling Techniques for    Uncertain Systems”, Birkhauser, 1994;-   B. Ninness and G. C. Goodwin, “Estimation of model quality”,    Automatica, 1995;-   M. Milanese, J. Norton, H. Piet-Lahanier, E. Walter (Eds), “Bounding    Approaches to System Identification”, Plenum Press, 1996;-   J. R. Partington, “Interpolation, Identification, and Sampling”,    Clarendon Press, 1997;-   H. Kimura, M. Milanese (Org.), Invited Session “Model Set Theory in    Identification and Control”, 38th IEEE CDC, Phoenix, 1999;-   J. Chen, G. Gu, “Control-oriented system identification: an    H-infinity approach”, John Wiley, 2000;-   Int. J. of Robust and Nonlinear Control, Special Issue on “Robust    control from data”, M. Milanese, M. Taragna Eds., 2004.

In addition to the above articles and books, contributions atinternational level for developing innovative methodologies andalgorithms about robust identification and control themes are documentedby further international literature; in particular, identificationmethods of approximate models of complex linear and non-linear systemsare dealt with by:

-   M. Milanese, G. Belforte: “Estimation theory and uncertainty    intervals evaluation in presence of unknown but bounded errors:    linear families of model and estimators”, IEEE Transactions on    Automatic Control, vol. 27, n. 2, April 1982.-   M. Milanese, R. Tempo: “Optimal Algorithms Theory for robust    estimation and prediction”, IEEE Trans. AC, August 1985.-   B. Z. Kacewicz, M. Milanese, A. Vicino: “Conditionally optimal    algorithms and estimation of reduced order models” Invited paper 2nd    Int. Symposium on Optimal Algorithms, New York, 1987. Also Journal    of Complexity ol. 4, pp. 73-85, 1988.-   M. Milanese, A. Vicino, “Optimal estimation theory for dynamic    systems with set membership uncertainty: an overview”, Automatica,    vol. 27, 997-1009, 1991;-   L. Giarrè, B. Z. Kacewicz, M. Milanese, “Model quality evaluation in    set membership identification”, Automatica, vol. 33, no. 6, pp.    1133-1139, 1997;-   M. Milanese, M. Taragna, “Optimality, approximation, and complexity    in Set Membership H-inf identification”, IEEE Transactions on    Automatic Control, vol. AC-47(10), pp. 1682-1690, 2002;-   M. Milanese, C. Novara, “Set Membership Identification of Nonlinear    Systems”, Automatica, Vol. 40/6, pp. 957-975, 2004;-   K. Hsu, M. Claassen, C. Novara, P. Khargonekar, M. Milanese, K.    Poolla, “Non-Parametric Identification of Static Nonlinearities in a    General Interconnected System”, International Federation Automatic    Control World Conference, Prague, 2005.

The robust control starting from experimental data is dealt with by:

-   M. Milanese, G. Fiorio, S. Malan, “Robust performances control    design for a high accuracy calibration device”, Automatica, Special    Issue on Robust Control, vol. 29, pp. 147-156, 1993;-   S. Malan, M. Milanese, D. Regruto and M. Taragna, “Robust control    from data via uncertainty model sets identification”, International    Journal of Robust and Nonlinear Control, Special Issue on “Robust    control from data”, 2004.

The robust control when there are saturations with wind-up preventingmethodologies and MPC is dealt with by:

-   M. Canale, M. Milanese, “Robust design of predictive controllers in    presence of unmodeled dynamics”, European Journal of Control, vol.    9, no. 5, 2003;-   M. Canale, M. Milanese, Z. Ahmad, E. Matta, “An Improved Semi-Active    Suspension Control Strategy Using Predictive Techniques”, Proc. IEEE    International Conference on Information & Communication    Technologies, Damasco, 2004; and their applications to different    application sectors are dealt with by:

M. Milanese, C. Novara, P. Gabrielli, L. Tenneriello, “ExperimentalModelling of vertical dynamics of vehicles with controlled suspensions”,SAE World Congress, Detroit, Mich., 2004;

-   M. Milanese, C. Novara, “Set Membership Prediction of River Flow”,    Systems and Control Letters, Vol. 53/1, pp. 31-39, 2004;-   A. Chiesa, “Tecniche di controllo Fault Tolerant per velivoli senza    pilota (UAV)” Graduating Paper, responsible M. Milanese, Politecnico    di Torino, 2004;-   M. Milanese, C. Novara, L. Pivano, “Structured SM identification of    vehicles vertical dynamics”, Mathematical and Computer Modelling of    Dynamical Systems (Special Issue), 2005.

However, from what is stated above, no systems and/or processes areknown for automatically controlling the flight of power wing airfoilswhich predictively operate, namely depending on observation andprevision of future flight conditions of the wing airfoils themselves,and which allow taking into account critical situations and errors dueto prediction.

Italian Patent Application n. TQ2003A000945, and European PatentApplication EP 04028646.0 which claims its priority, of the Applicantdisclose a system for converting the kinetic energy of Aeolian currentsinto electric energy through the predictive and adaptative control ofthe flight of power wing airfoils connected to a system of the“carousel” type. In such system, it would be desirable to use a systemand a process for automatically controlling the flight of used powerwing airfoils which allow driving in real time the wing airfoilsthemselves according to the modes described in the above Applications.However, in the current prior art, no systems are known which allowcontrolling the flight of wing airfoils used in the system of the“carousel” type in an efficient way.

Therefore, object of the present invention is solving the above priorart problems, by providing a system and a process for automaticallycontrolling the flight of power wing airfoils in a predictive wayaccording to a “preferred control strategy” based on observation andprevision of future flight conditions of the wing airfoils, taking intoaccount critical situations and errors due to prediction, allowing toavoid local maxima, oscillations and driving instabilities.

Another object of the present invention is providing a system and aprocess for automatically controlling the flight of the power wingairfoils used in the system of the “carousel” type described in ItalianPatent Application n. T02003A00945 and in European Patent Application n.EP 04028646.0.

The above and other objects and advantages of the invention, as willappear from the following description, are obtained with a system forautomatically controlling the flight of power wing airfoils as claimedin claim 1.

Moreover, the above and other objects and advantages of the inventionare obtained with a process for automatically controlling the flight ofpower wing airfoils as claimed in claim 27.

Preferred embodiments and non-trivial variations of the presentinvention are the subject matter of the dependent claims.

The present invention will be better described by some preferredembodiments thereof, provided as a non-limiting example, with referenceto the enclosed drawings, in which:

FIG. 1 is a block diagram showing the main components of the system forautomatically controlling the flight of power wing airfoils according tothe present invention;

FIG. 2 a is a diagram showing a reference system related to a power wingairfoil constrained to a known system of the “carousel” type;

FIG. 2 b is a graph showing the vector decomposition of a vector showinga gravity acceleration;

FIG. 3 is a diagram showing the navigation area of a power wing airfoilwith respect to direction and sense of an Aeolian current;

FIG. 4 a is a diagram showing a three-dimensional flight target of apower wing airfoil of the process according to the present invention;

FIG. 4 b shows a plan view of the diagram in FIG. 4 a;

FIG. 5 shows the diagram of FIG. 4 equipped with some parameters of theprocess according to the present invention; and

FIG. 6 shows a top view of the known system of the “carousel” type insome flight steps of a wing airfoil driven through the system and/or theprocess according to the present invention.

In the following description, the system and the process according tothe present invention will be described as preferably applied, merely asan example, to the automatic control of the flight of power wingairfoils used according to what is described in Italian PatentApplication n. T02003A000945 and in European Patent Application EP04028646.0. Consequently, due to obvious briefness questions, for adetailed description of the components which will be mentioned below andare common with the known system of the “carousel” type, reference mustbe made to the above Applications. It is however wholly clear that thesystem and the process according to the present invention can be usedalso for other applications, different from the system of the “carousel”type, by performing modifications which are anyway within the reach ofany skilled person in the art.

In such context, it is assumed that the flight of at least one powerwing airfoil is controlled by a driving unit equipped with alternatelymotored winches to which the airfoil itself is connected through tworespective driving cables, as described in T02003A000945 and in EP04028646.0.

With reference to FIG. 1 a, it is possible to note that the system 1 forautomatically controlling the flight of at least one power wing airfoil2 according to the present invention comprises:

first detecting means 3 on board the power wing airfoil 2 adapted todetect first pieces of information 3 a dealing with at least positionand orientation in space of the airfoil 2 itself and three-axesaccelerations to which it is subjected;

second detecting means 5 on the ground adapted to detect second piecesof information 5 a dealing with at least the amount of tension ondriving cables of the wing airfoil 2 and the position of thecounterweight of the driving unit 9;

processing and controlling means 7 of the first 3 a and second 5 apieces of information, adapted to transform the contents of such piecesof information into a mechanical drive operating on the winches of thedriving unit 9 to drive the wing airfoil 2 along a flight trajectorywhich maximises the “lift” effect generated on the wing airfoil 2 by theAeolian current in which it is immersed and maximises the amount ofkinetic energy subtracted from the Aeolian current; in fact it ispossible to demonstrate that, if the power wing airfoil is free ofscanning the wind front of the Aeolian current in a “lift” mode, notonly the traction which it can exert on the driving cables (andtherefore possibly on the “carousel” system arms) is enormously greaterthan the one exerted by keeping the wing airfoil still in the maximumwind resistance point by exploiting the “drag” effect, but the area inwhich the wing airfoils have a braking effect on the rotation of thepossible “carousel” system is wholly removed; in particular, theprocessing and controlling means 7 comprise a geometrical motor 7 aadapted to process such first pieces of information 3 a to returninformation 7 c about position, acceleration and orientation of the wingairfoil 2 to a numeric control 7 b, of a substantially conventionaltype, adapted to operate 9 a on the winches of the driving unit 9 tocontrol the traction force on the driving cables; and

a transmission system of the first pieces of information 3 a to theprocessing and controlling means 7, and in particular to the geometricalmotor 7 a.

Moreover, the system 1 according to the present invention could comprisean instability dissipation drive realised according to the robustcontrol theory.

In order to better understand the modes with which the first pieces ofinformation 3 a are directly collected by the first detecting means 3,which other pieces of information can be indirectly obtained from thefirst pieces of information 3 a and consequently which types of firstdetecting means 3 can be used in the system 1 according to the presentinvention, it can be useful to briefly examine the geometric piece ofinformation which characterises the position of the wing airfoil 2 inspace. With reference therefore to FIG. 2 a, it is possible to note thateach wing airfoil 2 which goes out of an arm 20 a of a system 20 of the“carousel” type of Applications T02003A000945 and EP 04028646.0describes, through the two driving cables 21 constraining it to theground and the imaginary line L which joins its ends, a triangle OABlaying on a plane in space. The aerodynamics study introduces theconcepts of roll, pitch and yaw, in general of the aircraft attitude. Incase of a wing airfoil 2, there is a constraint represented by theoutput nozzle of the driving cables 21 from the arm 20 a which compelsto renounce to the classical terminology (yaw, roll, pitch). Let us thentake into account an ideal reference coordinate system XYZ_(ref)integral with the arm 20 a of the system 20, so that the gravityacceleration has a component along only one axis Z. Let us further takeinto account the imaginary line which joins the arm 20 a end to themedium point of the wing airfoil 2. This segment, stated above,describes an angle α, with the horizontal plane XY_(ref), and an angle γwhich can be located starting from axis X_(ref) by projecting thesegment on the horizontal plane XY_(ref). Angles α and γ define theposition of the wing airfoil 2 in space. The geometric piece ofinformation is however complete only when the orientation concept isalso introduced. In order to define it, let us take into account againthe above described triangle. The triangle OAB lays on a plane whoseposition with respect to the ground reference system changes in timedepending on the wing airfoil 2 flight. The term orientation of the wingairfoil 2 therefore defines the angle β described by the plane on whichthe triangle and the horizontal plane XY_(ref) lay, apart from theangles α and γ. Though in order to deduce position and orientation ofthe wing airfoil 2 in space, an artificial ground optical view systemcan be adopted, this could be constantly impaired by the possibletransit of clouds or the lack of a limpid atmosphere, these problemsbeing still more felt if the system 1 is used together with the system20 of the “carousel” type characterised by high operating flight heightsof the wing airfoil 2.

Preferably, therefore, in order to deduce position and orientation ofthe wing airfoil 2 in space and accelerations to which it is subjected,the first detecting means 3 comprise three-axes accelerometers of theMEMS type in combination with at least one electronic compass. Thislatter one can be realised with a magnetometer, of the Fluxgate type oranother type, able to provide a reliable solution, much more accuratethan what could be obtained by the artificial view even under perfectvisibility conditions. In particular, the wing airfoil 2 is equippedwith at least one magnetometer and at least two three-axesaccelerometers placed at the ends of the wing airfoil, preferably nextto where the driving cables join the walls of the wing airfoil.Accelerometers on board the wing airfoil therefore solve the functionsof:

providing the system 1 with the capability of recognising position andorientation of the wing airfoil in space;

supplying multidimensional and instantaneous acceleration data, usefulfor the correct feedback of the control loop of the process according tothe present invention, described below, implemented through the system1;

correcting the possible false perception of the gravity vector, causedby strong aerodynamic accelerations.

Magnetometers complete the provision of pieces of information with theonly one which is necessarily not within reach of the system ofaccelerometers, namely the wing airfoil 2 rotation around the gravityaxis.

Accelerometers of the type used in the system 1 are sensitive to a widespectrum of accelerations, which range from static acceleration, such asgravity acceleration, to phenomena with frequency characteristics of afew kHz.

The three-axes accelerometer obviously defines a reference Cartesiansystem XYZ_(A) of its own, like the one shown in FIG. 2 b. By imaginingan instant in which such reference system coincides with the idealreference Cartesian coordinates system XYZ_(ref), the sensitivity togravity (static) acceleration allows de facto to distinguish anacceleration variation due to the only slanting of the accelerometer(which implies a variation of direction Z_(A) with respect to Z_(ref))from a variation due to the actual displacement of the reference systemXYZ_(A) origin, defined as aerodynamic acceleration and which representsthe flight of the power wing airfoil.

In general, the three-axes accelerometer will have a casual position inspace. The vector g which describes the gravity acceleration, with aconstant modulo, direction and sense, can therefore be decomposed intoits three components along the versors parallel to the three axes X_(A),Y_(A), Z_(A). Obviously, the gravity vector g position in thecoordinates system XYZ_(A) can also be expressed in sphericalcoordinates, depending on the angles φ and θ and the modulo of g (9.8M/s²), through the following change of coordinates:

X _(g) _(A) =g*cos φ*sin θ

Y _(g) _(A) =g*sin φ*cos θ

Z _(g) _(A) =g*cos θ

from which the following is obtained:

φ=a tan²(X _(g) _(A) ,Y _(g) _(A) )

θ=a sin(X _(g) _(A) )

where a tan² is the arc tangent(x) function with the ambiguityresolution (+/−)π/2.

Each accelerometer is subjected to two acceleration contributes. Thegravity acceleration, described above, is vectorily summed to theaerodynamic acceleration due to the actual motion of the wing airfoilwith respect to the fixed reference system XYZ_(ref). The firstdetecting means 3 can therefore be adapted to implement, in their ownintelligence aboard the wing airfoil, suitable algorithms whose purposeis distinguishing gravity acceleration from aerodynamic acceleration,communicating on one hand the spherical coordinates which point out thegravity vector decomposition with respect to the accelerometercoordinates system (and therefore the accelerometer slanting withrespect to the fixed reference system), and on the other hand, thereal-time evaluation of the aerodynamic acceleration. The measure ofsuch acceleration allows, first of all, to implement real-time controltechniques which are mandatory for promptly driving the flight of thewing airfoils, as will be seen afterwards in the description of thecontrol process according to the present invention. Such measure furtherallows instantaneously correcting the necessary angles φ and θ forevaluating the accelerometer orientation, while the acceleration dataintegration allows a further evaluation of the flight trajectory of thewing airfoil, de facto completing all information related to itsknowledge.

The need of providing the wing airfoil with at least two accelerometersderives from the fact that it is necessary to distinguish those wingairfoil movements which can be deemed as rotations around one of itsends. In this case, only one accelerometer assembled, for example, atthe wing airfoil centre, would perceive a tangential speed which can beapproximated with ν_(t)=ω·r, where ω is the rotation speed of therelevant circular motion, while r represents the accelerometer distancefrom the rotation centre (in this case, half the width of the wingairfoil). Such speed does not correctly describe the wing airfoilmotion, whose “free” end describes a circular trajectory with doubletangential speed ν_(t)=ω·r and centripetal acceleration equal toa_(c)=ν_(t) ²/r. The two accelerometers arranged on the wing airfoiltherefore realise an inertial six-axes platform with high performanceand high cutting frequency, which is able to recognise movements on sixaxes and describe position and orientation of the wing airfoil itself.

Rotations around an axis which do not imply variations in the axisdirection which is parallel to Z_(ref), can however be perceived by thisconfiguration of accelerometers only integratively. It is thereforenecessary to provide the wing airfoil with at least one magnetometer forcompensating the drift due to the double integration. The twoaccelerometers together with the output point of cables 21 from arm 20 adescribe a completely known triangle, the length of each side beingknown. The only unknown data is the angle included between arm and pairof cables 21 (consider the bisecting line of the acute angle includedbetween the two cables 21) projected on the horizontal plane XY_(ref).Such angle can be more comfortably evaluated from ground, by directlymeasuring it on the output point of cables from the arm.

As said, the second detecting means 5 are adapted to detect the secondpieces of information 5 a dealing at least with the amount of tension onthe driving cables of the wing airfoil 2 and the position, actual oremulated by the winches of the driving unit 9, of the counterweight; inparticular, function of the counterweight is potentially or electricallyabsorbing and storing the excess energy which can be generated due to atoo strong wind, and return it in the steps in which the wing airfoil isunder stall conditions with respect to the wind. The second detectingmeans 5 can therefore comprise “strain gauges” for measuring thedeflection of the driving cables and encoders on the winches of thedriving unit; such encoders, possibly associated with an alternatemotor, can also be used for detecting the length of the driving cableunwound from the winches, and consequently the distance from the wingairfoil to the driving unit, and the differential length between the twodriving cables of a same wing airfoil. Moreover, the second detectingmeans 5 can also comprise proximity sensors adapted to detect the anglebetween the driving cables at the outlet of the arm nozzle of the“carousel” system.

The second detecting means 5 can also comprise the optical or microwaveground artificial vision system, for the wing airfoil position. Theground optical view, with respect to the microwave one, has thenon-neglectable disadvantage of depending on the transit of clouds whichhide the wing airfoil from view. An efficient artificial view systemhowever provides an important contribution in terms of safety, supplyingnecessary information to avoid collisions with helicopters and smallaircrafts in general.

From the first 3 a and second 5 a pieces of information respectivelymeasured by the first 3 and second 5 detecting means, the wing airfoilposition in space can anyway be obtained in at least three differentways:

a) processing of data coming from accelerometers and magnetometersthrough the geometrical motor; in particular, the length of the wingairfoil position vector can be obtained through the double integrationof the acceleration signal;b) combining data which can be obtained from winches encoders with themeasure of angles between cables and arm which can be obtained at thearm end; it must be noted that from the arm end, only the angles whichthe pair of driving cables, as a whole, generate with the arm itself canbe evaluated;c) using the artificial view system: in this case, however, to the delayof deriving information, the delay due to acquiring and composing theimages must be added.

Similarly, the wing airfoil orientation in space can be obtained both byprocessing accelerometer data and by means of the artificial viewsystem.

Acceleration, instead, must necessarily be obtained on board the wingairfoil, due to the fact that the delay introduced by computing thesecond derivative from the position is incompatible with the real-timecontrol techniques which are mandatory for driving the wing airfoilsflight. This implies that intelligence on board the wing airfoil becomesan integral part of the control system 1.

In an alternative embodiment, it is also possible to provide for the useof Theological polymers in the wing airfoil structure, with the purposeof realising actuating systems directly on board; in such case, it ispossible to provide that the first detecting means comprise othersensors which are able to provide signals derived by feedback fromcomposite materials in order to contribute or detect the wing airfoilposition in space.

Due to what is stated above, the measure of wing airfoil position andorientation is therefore apt to be redundant, in particular, theacceleration evaluation starting from direct position and orientationinformation, though not being efficient in terms of real-timeredundancy, can contribute to form the diagnostic redundancy of thesystem for evaluating the flight characteristics of the wing airfoil.

In this context, particular relevance can be given to inventivemethodologies for designing virtual sensors placed together with thefirst and/or second detecting means of the system 1. Actually, many ofthe quantities measured by the sensors of the first and second detectingmeans could, in case of failure of the specific sensor, also beestimated from the measures of the other sensors throughobservers/Kalman filters designed depending on an adequate model of thedynamic behaviour of wing airfoils. The advantages of being able toperform desired redundancy levels by using virtual sensor in place ofsome of the real sensor is evident, in general depending on physicalsensor costs and on problems about installation and communication withthe control system. These advantages are particularly relevant forsensors on board the wing airfoils, in which advantages are added interms of weight and energy consumption. In such sense, experiences canbe integrated deriving from the application of virtual sensors in theaeronautic field, as described in “Rilevazione, isolamento e recupero ofthe guasti of the sensori di assetto di aeromobili”, Graduation Thesis,Responsibles: M. Milanese (Dip. Automatica e Informatica), S. Chiesa(Dip. Ingegneria Aerospaziale), M. Birindelli (Alenia), Politecnico diTorino, 2003 by E. Corigliano, and in the automotive field, as describedin “Experimental results in vehicle sideslip angle estimation” SAE 2006,Detroit di M. Milanese, D. Regruto, e A. Fortina.

The numeric control 7 b which drives the wing airfoils needs reliableand real time acceleration and position information. In particular,three-axes accelerations which describe the behaviour, in thethree-dimensional space, of the wing airfoil, must necessarily beacquired on board the wing airfoil itself, therefore at a height.

It follows the need that the transmission system of the first pieces ofinformation 3 a between wing airfoil and processing and controllingmeans 7 complies with strict specifications in terms of performance andenergy absorption. In order to comply with such requirements, andpreferably excluding the most obvious galvanic connection between wingairfoil and ground processing and controlling means 7 not to realise afavourable path for possible atmospheric discharges, the transmissionsystem can be integrated in the driving cables of the wing airfoilthrough at least one data optical fibre.

The insertion of optical fibres in cables must however take into accountthat the driving cables are generally with a high modulus fibre and thatthe working environment is difficult both for kevlar and for UHMWpolyethylene. As known, the kevlar can have seepages and tend to absorbwater, which could imply an increase of electric conductivity in case ofacid rains or local pollutants, making it necessary to use protectingsheaths or braids, for example made of THFT, which would also perform anabrasion-prevention function. In this case, the natural placement of theoptical fibre would be between sheath and bundle of fibres, payingattention to give a certain freedom in length in order not to subjectthe optical component to the same elastic distortions of the cable.

In case of UHMW polyethylene, the considerations given for kevlar remainvalid, but the problem of its application must be added, the so-called“creep”, namely the irreversible elongation in time under efforts, whichwould impose a frequent replacement of cables equipped with opticalfibres thereby reducing the actual working time. There are howevermaterials which can be associated with polyethylene, which reduce theproblem, which can be taken into account in combination with thepossible weaving of the optical fibre inside the UHMW bundle itself. Itis however necessary to underline that the section increases with thediameter square, and therefore the cables workload should be easilydimensioned depending on the maximum required force, without incurringin creep and without increasing the aerodynamic drag force, namely theresistance that the cables give to air penetration. Moreover, a wingairfoil geometric modelling of the cable section in order to make themassume shapes with lower drag and more lift could be a useful solution.

Other optical fibres in cables could be used for power supplying thefirst detecting means on board the wing airfoil. Introducing, in amultimode low-loss fibre, a sufficient amount of light on the groundside, light could be reconverted through a micro photovoltaic module,for example made of GaAS, on the wing airfoil side.

Alternatively, the transmission system can allow the transmission of thefirst pieces of information in radio-frequency, such solution certainlyappearing as the most natural method for a communication which needsavoiding electric connections, but can be demanding from the energeticpoint of view.

Even if the optical fibres solved the transmission of information, itcan anyway be mandatory to keep the additional resource represented bythe radio-frequency transmission for redundancy reasons. If the radiocommunication represents therefore a backup solution with respect to thecommunication through optical fibres, a watchdog could command itsactivation, being careful to possible interruptions of optical flowacknowledgements.

Obviously, the radio-frequency transmission system can use an extremelywide variety of communication protocols to send the first pieces ofinformation to the ground processing and controlling means. By using forexample a monodirectional continuous stream protocol, the lowcommunication level, the physical layer, would be the radio-frequencymediator, which can be a simple FSK modulator of digital informationprovided by sensors and continuously active, however implying acontinuous energy absorption. It is however possible to provide somesolutions for reducing necessary time and power for transmittinginformation, such as what follows:

high-gain directional antennas: an antenna which does not add resistanceto the air flow can be obtained with leads complying with existinggeometries: the suitable places can be the length of cable next to thewing airfoil, or the wing airfoil wall. These two placements would havethe advantages of being always directed towards the driving unit, whichwould house the corresponding receiving antenna communicating with theprocessing and controlling means;

carrier suppression: it is a solution known as single side bandtransmission which allows high energy savings, however reducing thebit-rate which can be transmitted;

asynchronous activation: this solution requires a special software onboard the transmitter which evaluates the meaning of data stream,transmitting information only in the most meaningful times, by adoptingthe concept of video compression key frames. The advantage would beimportant, because energy demand reduction factors could be obtainedwhich can be computed similarly to data compression factors.

Alternatively, a datagram packet protocol can be used, like the onewhich is used in Internet for transferring data flows without thecharacteristic sequence and validity checks, suitable for films andradio broadcasting. Since the protocol is bi-directional, the burden ofchecking communication rhythm and related electric absorption could betransferred to the receiving station control, which could query thesensors only in case of need or to re-align the dynamic model of thecontrol system with the real status.

Alternatively, an asynchronous negotiated transport protocol can beused, which is more complex to implement, but is able to join togetherall advantages of the above described solutions. It is in fact a verylight and nervous bi-directional protocol which could originate thecommunication both from the first detecting means side and from theprocessing and controlling means side. The absence of a stack bringsabout the fact of not having latencies which could impair the bit-rate.

In a further alternative, it is possible to provide for the use of anultrasound transmission system.

Anyway, the two accelerometers together with the magnetometer on boardthe wing airfoil produce seven information flows at thousands of samplesper second. Such stream of raw data from the wing airfoil towardsground, in addition to be excessive for transmission, is substantiallyuseless for the geometrical motor: the geometrical motor must inpractice cycle with a frequency compatible with system size and timeconstants, continuously providing the updated position data to thenumeric control, and pretends more reasoned data as input. For suchpurpose, it can be provided to use pre-processing means 11 adapted toperform a pre-processing of all or part of the first pieces ofinformation 3 a on board the wing airfoil to provide pre-processed firstpieces of information 3 a′ adapted both for transmission and for aneasier processing by the geometrical motor 7 a. For such purpose, theaccelerometers can be equipped with integrated pre-processing DSP(Digital Signal Processing) means 11.

Moreover, as previously stated, the accelerometers of the MEMS type usedfor collecting useful information for knowing the flight trajectory ofthe wing airfoil are sensitive both to static accelerations (gravity)and to dynamic accelerations. Having to use the gravity (static)acceleration for measuring useful angles for obtaining position andorientation of the wing airfoil, there occurs the problem of insulatingthe static acceleration from intense aerodynamic accelerations to whichthe wing airfoil is subjected. This activity can be performed by asuitable algorithm which must necessarily cycle at speeds which areincompatible with the transmission speed made available by thetransmission system and must therefore be implemented by thepre-processing means 11 on board the wing airfoil.

The system 1 according to the present invention further comprises atleast one supplying system of the first detecting means and of thecomponents of the transmission system on board the wing airfoil;obviously, such first means and components could be self-suppliedthrough their own batteries. It is however necessary to take intoaccount the fact that the system 1 according to the present invention,above all if used in association with the “carousel” system, couldrequire very high energy autonomies, in order to avoid to have to takethe wing airfoil to ground with too much a frequency to replace orrecharge the batteries, with the consequent burden of having to stop theoperation of the “carousel” system. Moreover, it is useful to take intoaccount that the system 1 should be able to operate in contact withnatural forces and events, such as rain, snow, ice, great windvariations, atmospheric discharges, day, night, sun. In order to makeavailable the limited energy demand on board the wing airfoil,alternative solutions have been provided to the self-supply, whichexploit sun and apparent wind elements. The supplying system in fact cancomprise photovoltaic thin-film modules, on a plastic support, which canbe advantageously applied on the wing airfoil without modifying itsaerodynamic characteristics and weight. These modules should obviouslyproduce a sufficient amount of energy to supply the on-boardelectronics, increasing the recharging capability of possibleaccumulators during the night.

Alternatively, it is possible to exploit the apparent wind flow which isalways available around the wing airfoil; the supplying system couldtherefore comprise at least one Aeolian micro-turbine keyed-in to asmall permanent magnet generator and supplied by the apparent wind.

The present invention further refers to a process for automaticallycontrolling the flight of power wing airfoils, preferably through asystem 1 like the previously described one. In particular, the processaccording to the present invention operates predictively according to a“preferred control strategy” based on the observation and prediction offuture flight conditions of the wing airfoils, taking into accountcritical situations and errors due to prediction, allowing to avoidlocal maxima, oscillations and wing airfoil driving instability. Aspreviously seen, the system 1 according to the present invention isconfigured in such a way that the processing and controlling means 7acquire as input information such as position, accelerations, forces andother geometrically defined quantities, process them, and as outputoperate on the winches which control the flight trajectory of the wingairfoil.

In order to better describe the logic for implementing the processaccording to the present invention, it is useful to deal again with thebehaviour dynamics of the wing airfoil. With reference in particular toFIG. 3, it is possible to schematically note the conditions of the windfront or of the Aeolian current W which the wing airfoil 2 is able tointercept, in following instants, with respect to a reference integralwith the constraint point of the driving cables 21 to ground. FIG. 3describes, in fact, a quarter of a sphere which is the navigation areaof the wing airfoil 2, at the centre of which the so-called “powerzone”31 is defined, in which the wing airfoil 2 expresses the maximumtraction on driving cables 21. By going away from the “powerzone” 31,through a zone 32 of the window which can be navigated by the wingairfoil 2 in which the traction on the driving cables 21 isprogressively reduced, an edge 22 of the window which can be navigatedby wing airfoil 2 is reached, in Which the traction on the drivingcables 21 is highly reduced.

With reference to FIGS. 4 a and 4 b, imagine now to take into account,in the current instant, the wing airfoil 2 placed at the centre of anideal “target” plane P, univocally defined as normal to the bisectingline of the angle formed by the two driving cables 21. The processaccording to the present invention, by operating through the system 1,can decide if the wing airfoil 2 must perform any one of the possibleflight trajectories TV₁, TV₂, TV₃, . . . , TVn, starting from thecurrent position at the centre of plane P. On this plane P, it ispossible to divide the flight trajectories which the wing airfoil 2 cantravel depending on the necessary time T₀, T₁, T₂, . . . , Tn, to reacheach point. In particular, it is possible to take into account followingtime intervals which correspond to following angular positions of thearm 20 a of the “carousel” system 20. The flight trajectory of the wingairfoil 2 will thereby occur synchronously with the arm 20 a movement.

For easiness, let us consider in particular FIG. 4 b with coordinatesrelated to the wing airfoil 2. The Cartesian reference system isintegral with the wing airfoil 2 and, with it, it moves into space. Thewing airfoil 2 is therefore always at the centre of plane P. Only timesflow. The diagram does not point out the point in which one has to go,since it is a future evaluation. When the first time interval T₀ haselapsed, the reference system integral with the wing airfoil draws againa “target” which is wholly similar to the previous one, with the onlydifference that time T₁ has become T₀, and so on. T₁ representstherefore the set of points which can be reached by the wing airfoil 2in its flight trajectory in 1 step, T₂ the set of points which can bereached in 2 steps, and so on. The wing airfoil 2 is anyway always atthe centre of the “target” plane P.

For easiness, FIGS. 2 a and 2 b show as an example the “target” plane Ptill time T₂, but obviously the number n of steps which can be observedcan be different.

In order to evaluate its own control strategies and choose a flighttrajectory which the wing airfoil must perform, the process according tothe present invention uses flight and control parameters.

With reference therefore to FIG. 5, it is possible to note the “target”plane P on which some flight and control parameters are graphicallyincluded for the process according to the present invention.

FIG. 5 shows how the parameters in simplified form change in space,having reduced the complexity of roto-translations of the “carousel”system in a model integral with the reference system of the wing airfoil2. Morphology and characteristics of such parameters are an essentialpart of the information which allow the control to decide the flightstrategy of the wing airfoil 2. It is in fact possible in this way torepresent optimal motion, direction and position for reaching the idealheight Q in order to have the best wind, or which is the best angle ofincidence with respect to the wind, but at the same time it is possibleto represent other parameters, such as for example desirable maximumtraction area T, interdiction areas ZI (areas in which there are, forexample intolerable structural stress situations, instability, excessiveforces) and the functional parameters of the system 1, such as areas inwhich the counterweight C, which is used to keep the flight parametersof the wing airfoil 2 constant and to quickly adjust the driving cableslength (dynamic length), is kept at half its own dynamics. The graph Ccorresponding to the counterweight, for example, can assume usefulpositions to lift the counterweight or to make it descend. Also thedriving unit winches could be subjected to parameters, since they pointout the absolute cables length. The graph of the height parameter Q,instead, represents the optimum area for height problems. The graph ofthe manoeuvre parameter M, instead, represents the optimum area toperform the most important manoeuvre in the flight of the wing airfoil 2defined as azimuth gybing, which consists in a sudden manoeuvre duringwhich the wing airfoil 2 is driven into a quick transition betweenflight traverses. With particular reference to FIG. 6, it is possible tonote that, in general, if the power wing airfoil 2 is free of scanningthe wind front, not only is the traction which it can exert on thedriving cables (and therefore on the arms of the “carousel” system 20)much greater than the one exerted keeping the wing airfoil unmoving inthe maximum wind resistance (drag) point, but the area in which the wingairfoils have a braking effect on the “carousel” system 20 rotation iscompletely removed. In the upwind area 37, or bowline, the capability ofdriving the flight of the wing airfoil 2 allows performing the azimuthgybing, which consists in a quick transition between the two traverses36 and 38, during which the wing airfoil 2 travels in air a distanceequal to at least three times the arc of circumference 34 affected intime in which the “carousel” system 20 travels along such arc. Theflight control must take care that the manoeuvre, in addition to bequickly performed, has in no way a negative influence in producingenergy. In FIG. 6, the position of each wing airfoil is random, namelythe image has to be deemed as a top snapshot of the operation of the“carousel” system. In this configuration, each wing airfoil is free ofsearching the maximum wind intensity, avoiding the exhausted wind frontareas for the passage of the immediately previous wing airfoil.

The dimension of each graph (height, counterweight, etc.) isproportional to the allowed tolerance to the related parameter. Eachparameter has in turn a relative weight P_(Q), P_(C), P_(M), P_(ZI),P_(T), a relative height with respect to all heights, which will bedescribed below.

From the plane P shown in FIG. 5, once having performed the manoeuvreand the time interval T₀ has elapsed, one passes to a new plane P,re-computed for the following decision. If global situations areconstant, the graphs related to each parameter tend to be concentrated.The choice of graphically representing the optimum areas for eachconsidered parameter is the method for solving the ambiguities andunderstanding which decision must be chosen. Such strategy is useful notto fall in local maxima, namely positions which seem to be the best, butthey are not.

The process has always information available, in a direct form or a formderived from the first and second pieces of information detected by thedetecting means of the system 1, related to the flight height of thewing airfoil, to the counterweight dynamics, to traction values, to thesafety computation in interdiction areas, to the time in whichmanoeuvres must be made. Let us take into account, for example, the mostimportant manoeuvre in the flight of the wing airfoil, which has beendefined as azimuth gybing. Deciding whether to perform it can be atriggered event: under such conditions, in fact, the process accordingto the present invention can provide for an emergency step in which thewing airfoil is shown which manoeuvre must be done with maximumpriority. It is not to be excluded that a far-sighted strategyautomatically devises the manoeuvre without the need of suggesting it.If a good evaluation time depth is reached, the gybing will occur at anideal time computed depending on current information and parameters,since presumably this is the most intelligent action not to removetraction, not to lose dynamics on the counterweight and to comply with acertain height without going into interdiction areas.

The process step, which decides at every step which direction the flighttrajectory of the wing airfoil can take, can be visually represented asa matrix, like the one in the following Table 1, containing, for eachparameter, the best coordinates XY at times T₀, T₁, T₂, . . . , Tn, onthe normal plane with respect to the driving cables barycentre.

TABLE 1 Parameter Weight T₀ T₁ T₂ . . . T_(n) Height P_(Q) QX₀Y₀ QX₁Y₁QX₂Y₂ . . . QX_(n)Y_(n) Counterweight P_(C) CX₀Y₀ CX₁Y₁ CX₂Y₂ . . .CX_(n)Y_(n) Traction P_(T) TX₀Y₀ TX₁Y₁ TX₂Y₂ . . . TX_(n)Y_(n)Interdiction P_(ZI) ZIX₀Y₀ ZIX₁Y₁ ZIX₂Y₂ . . . ZIX_(n)Y_(n) areasManoeuvre P_(M) MX₀Y₀ MX₁Y₁ MX₂Y₂ . . . MX_(n)Y_(n) Resultant RX₀Y₀RX₁Y₁ RX₂Y₂ . . . RX_(n)Y_(n) PT PT₀ PT₁ PT₂ . . . PT_(n)

The matrix in Table 1 therefore contains desired data. The differencebetween current height and desired height can make one access thenumeric controls logic, or the errors computation. This characteristicis intrinsic in the matrix: substantially, there are current coordinatesand desired coordinates for T₀, T₁, T₂, . . . , Tn. All parameterstreated in the matrix create pairs of values XY for a time instant T₀,T₁, T₂, . . . , T_(n). The process then photographs the situation inwhich the wing airfoil is, and transforms the plane P in FIG. 5 intonumbers and coordinates. Taking into account, for example, the heightproblem, the matrix value QX₀Y₀ points out a point in the neighbourhoodof the height parameter, tending to the centre of the graph of height Qin FIG. 5. The circular shape makes all agree in times, in which thetrend is clear: rise in T₁, T₂. In case of traction, the process couldalready compute the evolution of the ideal point in time: the form ofthe desired data therefore is not circular.

Obviously, the relative weight P_(Q), P_(C), P_(M), P_(ZI), P_(T) ofevery related parameter Q, C, M, ZI, T can be settable, and such settingcan be dynamic (retroactive). By analysing, for example, the mean errorof the desired height with respect to the current height, etc., theprocess can be aware of the most difficult parameters to be satisfied. Aretroactive process corrects the weights of the most criticalparameters, in such a way as to make decisions about such parametersmore important. This type of error can be given a measure, for example apercentage measure, standardised for every parameter with respect to amaximum error value. For example, if in time the counterweight is alwaysoutside the dynamics centre and risks to arrive to its end-of-stroke,this standardisation allows locating which is the parameter that makesmost mistakes. It can be an independent process which adjusts theweights of each parameter.

Once having collected the best coordinates for each parameter, theprocess provides for a step in which the vector sum of all coordinatesat time T₀ is computed. The resulting vector is RX₀Y₀, which is stillnot the direction of the flight trajectory in which the wing airfoil hasto be moved, since the forecast for the future is still to beconsidered. The process then computes the vectorial sums for all futuresteps RX₁Y₁, RX₂Y₂, . . . , RX_(n)Y_(n) and time weights PT₀, PT₁, PT₂,. . . , PT_(n), are then introduced, which give priority to short-termstrategies, at the same time avoiding to take the wing airfoil inpotentially critical areas.

Obviously, also the time weights PT₀, PT₁, PT₂, . . . , PT_(n) can besettable.

Through the computation of the matrix in Table 1, the process accordingto the present invention locates an ideal instantaneous coordinate(target) to which one tends with the manoeuvre of the wing airfoil alongits flight trajectory. Once having found the ideal coordinate, it isnecessary to take care of the manoeuvre and of the control of thedriving cables in order to make the wing airfoil reach its target. Theprocess then comprises a step of choosing the best path (shortest path,by-passing the interdiction areas, etc.) in order to take the wingairfoil from the current position to the target. In this step,therefore, the process decides, depending on the target to be reached,the best flight trajectory for reaching it minimising the time, sincebeing with the wing airfoil always correctly on the target sequencelocated as best, is a guarantee of producing the maximum energy undermaximum safety and the maximum compliance with dynamic specifications.The heart of the problem in this step is how transferring the targetcoordinates in traction. The step of choosing the best path thereforeuses an Inertial Navigation System (INS) supported by a dynamic model ofthe wing airfoil (FVM) taking into account wing airfoil flight equationsand inertias, together with the percentage of reaction which it can havedepending on the traction differential on cables. Inertias and tractiondescribe the manoeuvre law of the wing airfoil; it is suitable to takeinto account the (predictive) evaluations of the best path, byevaluating all possible paths and evaluating the manoeuvre, with adecision tree. In this step, apparent speeds and tractions are takeninto account, and one is able to accurately evaluate the best pathstrategy. Synergy between inertial navigation and information given bydynamic modelling, namely the motion model obtained from the history ofthe wing airfoil positions, from control inputs and from forcesoperating on the wing airfoil itself have been widely demonstrated inthe past by using dynamic equations of the vehicle (for example byKoifman and Bar-Itzhack, 1999; Ma et al., 2003). These studiesdemonstrate that the main advantage in using a vehicle model is theimprovement of the capability to observe the error sources in the INS.

In the Inertial Navigation System INS, position (ρ_(n)), speed (v_(n))and Eulero angles (ψ) of the wing airfoil, referred to a referencesystem n=[N, E, D] (North, East, Down) are computed as follows:

{dot over (p)}_(n)=v_(n)

{dot over (v)} _(n) =C _(b) ^(m) f _(b) +g _(n)

{dot over (Ψ)}=E _(b) ^(n)ω_(b)

where g_(n) is the gravity acceleration, f_(b) is the accelerationvector on the three axes, ω_(b) is the rotation. C^(n) _(b) and E^(n)_(b) are respectively the transformation and rotation matrices, definedas follows:

$C_{b}^{m} = \begin{bmatrix}{c_{\psi}c_{\theta}} & {{c_{\psi}s_{\theta}s_{\varphi}} - {s_{\psi}c_{\varphi}}} & {{c_{\psi}s_{\theta}c_{\varphi}} + {s_{\psi}s_{\varphi}}} \\{s_{\psi}c_{\theta}} & {{s_{\psi}s_{\theta}s_{\varphi}} + {c_{\psi}c_{\varphi}}} & {{s_{\psi}s_{\theta}c_{\varphi}} - {c_{\psi}s_{\varphi}}} \\{- s_{\theta}} & {c_{\theta}s_{\varphi}} & {c_{\theta}c_{\varphi}}\end{bmatrix}$ $E_{b}^{''} = \begin{bmatrix}1 & {s_{\varphi}t_{\theta}} & {c_{\varphi}t_{\theta}} \\0 & c_{\varphi} & {- s_{\varphi}} \\0 & {s_{\varphi}\sec_{\theta}} & {c_{\varphi}\sec_{\theta}}\end{bmatrix}$

where s(.), c(.) and t(.) represent sen(.), cos(.) and tan(.), whileΨ=[φ, θ, ψ] are the Eulero angles.

The dynamic model of the wing airfoil (FVM) with six degrees of freedomis instead composed of a set of equations which provide for statevariables of the wing airfoil, composed of position, speed, Euleroangles and rotations by means of the control variables of the wingairfoil, which are assumed as known from system 1. The movement of thewing airfoil can be described by the following system of movementequations, in which the forces operating on the vehicle are function ofwing airfoil position, speed, Eulero angles and current rotation:

{dot over (u)}=rv−qw+g _(x) +[Fx/m]

{dot over (v)}=pw−ru+g _(y) +[F _(y) /m]

{dot over (w)}=qu−pv+g _(z) +[F _(z) /m]

{dot over (p)}=C ₃ pq+C ₄ qr+C ₁ l+C ₃ N

{dot over (q)}=C ₇ pr−C ₆(p ² −r ²)+C ₅ M

{dot over (r)}=C ₉ pq−C ₃ qr+C ₂ l+C ₈ N

where v_(b)=[u, v, w] are the speed components along the three axes inthe wing airfoil reference system, ω_(b)=[p, q, r] are the wing airfoilrotations, F_(x), F_(y), F_(z) and It M, N are the components of theforce and of the moments acting on the wing airfoil along its own axes.g_(x), g_(y), g_(z) are the components of the gravity accelerationvector decomposed in the wing airfoil reference system, whose mass isdesignated as m. Coefficients C₀₋₉ are obtained starting from theinertia matrix I.

For example, there can be two methods through which the dynamic model ofthe wing airfoil FVM can be applied as support to the InertialNavigation System: a first method implies the comparison and correctionof speed and attitude of the wing airfoil such as are obtained,independently, from INS and from FVM. The second method uses theacceleration and rotation forecast performed by the FVM in order torealise a direct calibration of the Inertial Measuring Unit (IMU). Inboth cases, the INS processes wing airfoil position, speed and Euleroangles (which describe the rotation) for integrating acceleration androtation measures provided by the IMU on board the wing airfoil. In thefirst method, however, the wing airfoil model computes wing airfoilspeed and angles by using the control inputs of the aircraft itself.Moreover, the real implementation of FMV and INS takes advantage fromthe application of the most recent developments of the mathematics basedon quaternions. Task of an Extended Kalman Filter (EKF) is evaluatingINS and FVM errors by observing the differences between speed and anglesdata respectively produced by INS and FVM.

In the second method, instead, the FMV is used for computingacceleration and rotation estimation directly from control inputs. Theinput of the Extended Kalman Filter is therefore composed of differencesbetween acceleration and rotation estimations computed by FVM and thoseread from used sensors. The EKF is therefore used for estimatingacceleration and rotation errors of sensors and FVM, which are then usedfor consequently correcting sensors and FVM.

The wing airfoil manoeuvre has however the problem of being calibrated.It is true that one can decide the amount of manoeuvre, but the amountremains to be defined. There is in fact the risk of oscillating, in anexcessive gain, due to inertial causes, kinematic chain elasticity(winches are on the ground, the manoeuvre occurs in air) and measurementdelay (neglectable). There is therefore the risk of performingnon-calibrated, insufficient or exaggerated manoeuvres, which compel toperform continuous corrections (opposite compensation), with the risk ofuncontrollably oscillating. In order to solve this group of problems,the control art has already devised techniques such as Hinf and thealready mentioned Kalman Filters, which consider the actuation delay asone of the disturbances, one of the noises which the control mustmanage, by optimising the manoeuvre and limiting it with filters andmethodologies which are calibrated on the system or self-calibrating.The described process according to the present invention can be equippedwith predictive capabilities whose time depth is function of theinformation processing power of the system according to the presentinvention. The other major characteristic which allows forecasting theabove described problems is that the processing and controlling meansreceive acceleration-related information. An excessive manoeuvre istherefore perceived largely beforehand with respect to when the movementoccurs and this should bring the system to a sub-critical situation, inwhich oscillations can be not triggered due to the capability of sensorsof providing data 180° in advance of the movement. Should a positiondata be directly available, a new operation would be performed once adamage has been done, while the acceleration announces the damage.

Due to what has been stated above, the process according to the presentinvention therefore comprises the steps of:

a) detecting the first pieces of information 3 a through the firstdetecting means 3 related to a current instant of the flight trajectoryof the wing airfoil; possibly re-processing all or part of the firstpieces of information 3 a through the pre-processing means 11 to obtainthe pre-processed first pieces of information 3 a′;b) detecting the second pieces of information 5 a through the seconddetecting means 5 a related to a current instant of the flighttrajectory of the wing airfoil;c) sending through the transmission system the first pieces ofinformation 3 a, 3 a′ to the processing and controlling means 7, inparticular to the geometrical motor 7 a;d) sending the second pieces of information 5 a to the processing andcontrolling means 7, in particular to the geometrical motor 7 a;e) from the first 3 a, 3 a′ and the second pieces of information,directly or indirectly obtaining values related at least to currentposition XY and current flight height of the wing airfoil, tocounterweight dynamics, and to traction on driving cables;f) defining flight and control parameters, such as for example height Q,counterweight dynamics C, manoeuvre M, interdiction areas ZI, Traction Tof the driving cables; possibly defining a tolerance for each one ofsuch parameters;g) defining a relative weight P_(Q), P_(C), P_(M), P_(ZI), P_(T), foreach one of the flight and control parameters;h) computing for each parameter the best coordinates XY in followingtimes T₀, T₁, T₂, . . . , T_(n) i) computing the vectorial sum RX₀Y₀ ofall coordinates at time T₀;j) computing the vectorial sums RX₁Y₁, RX₂Y₂, . . . , RX_(n)Y_(n) forall future times T₁, T₂, . . . , T_(n);k) defining and applying the time weights PT₀, PT₁, PT₂, . . . , PT_(n),for the vectorial sums;l) choosing the best among RX₁Y₁, RX₂Y₂, . . . , RX_(n)Y_(n) as idealinstantaneous coordinate (target) to which the wing airfoil manoeuvremust tend;m) choosing the best flight trajectory path TV₁, TV₂, TV₃, . . . ,TV_(n), to take the wing airfoil from the current position to thetarget;n) taking the wing airfoil from the coordinates of the current positionto the target by acting on the driving unit through the numeric control7 b of the system 1; preferably using an Inertial Navigation System(INS) supported by a dynamic model of the wing airfoil (FVM);o) repeating the steps a) to n) at every time interval Δt defined ascontrol loop frequency; it can be provided that the process according tothe present invention also comprises a step of retroactively adjustingthe length of Δt, making de facto the loop frequency adjustable. If Δtis short, the process will perform an accurate and detailed, butpossibly exuberant and scarcely far-sighted, short-term predictiveanalysis, since the n steps possible in time do not globally reach anoptimum time distance from the current instant: it becomes thereforenecessary to relate the steps of forecasting the future with the steplength, in order to optimise the time depth of the flight path of thewing airfoil to be performed. It is therefore suitable to evaluate theopportunity of performing a forecast which covers too much in thefuture: it is reasonable to assume that providing more than onerevolution of the “carousel” system is useless, since, under stabilityconditions, the situation is repeated. The ideal length of Δt isprobably the one which corresponds to the length of a complex manoeuvre,such as the azimuth gybing of the wing airfoil.

1. A system for automatically controlling a flight of at least one powerwing airfoil, the power wing airfoil being controlled by a driving unitequipped with two winches to which the power wing airfoil is connectedby means of two respective driving cables, the system comprising: firstdetecting means on board of the power wing airfoil adapted to detectfirst pieces of information dealing with at least one position and oneorientation in space of the power wing airfoil and accelerations towhich said the power wing airfoil is subjected; second detecting meanson the ground adapted to detect second pieces of information dealingwith at least one amount of a tension on the driving cables of the powerwing airfoil and a position of a counterweight of the driving unitprocessing and controlling means of the first and the second pieces ofinformation, adapted to transform a contents of the pieces ofinformation into a mechanical drive operating on the winches of thedriving unit to drive the power wing airfoil along a flight trajectoryTV₁, TV₂, TV₃, . . . , TVn maximising a lift effect generated on thepower wing airfoil by an Aeolian current W in which it is immersed andmaximising an amount of kinetic energy subtracted to the Aeolian currentW; and a transmission system of the first pieces of information to theprocessing and controlling means.
 2. A system of claim 1, wherein theprocessing and controlling means comprise a geometrical motor adapted toprocess the first pieces of information in order to return position,acceleration and orientation information of the wing airfoil to anumeric control adapted to operate on the winches of the driving unitfor controlling a traction force on the driving cables.
 3. A system ofclaim 2, wherein the transmission system transmits the first pieces ofinformation to the geometrical motor.
 4. A system of claim 1, the systemcomprising an instability dissipation drive.
 5. A system of claim 1,wherein the first detecting means comprise three-axes accelerometers. 6.A system of claim 5, wherein the three-axes accelerometers are of theMEMS type.
 7. A system of claim 1, wherein the first detecting meanscomprise an electronic compass.
 8. A system of claim 7, wherein theelectronic compass is a Fluxgate magnetometer.
 9. A system of claim 5,wherein each one of two of the three-axes accelerometers is placed in arespective end of the wing airfoil next to a union of the driving cableswith the walls of the wing airfoil.
 10. A system of claim 1, wherein thesecond detecting means comprise strain gauges adapted to measure adeflection of the driving cables.
 11. A system of claim 1, wherein thesecond detecting means comprise encoders on the winches of the drivingunit.
 12. A system of claim 1, wherein the second detecting meanscomprise proximity sensors.
 13. A system of claim 1, wherein the seconddetecting means comprise a ground artificial vision system.
 14. A systemof claim 1, wherein the wing airfoil is made of rheological polymers.15. A system of claim 1, wherein the first or second detecting meanscomprise virtual sensors.
 16. A system of claim 1, wherein thetransmission system is integrated in the driving cables of the wingairfoil through at least one data optical fiber.
 17. A system of claim1, wherein the driving cables have a wing airfoil-shaped section.
 18. Asystem of claim 1, wherein the transmission system is of theradio-frequency type.
 19. A system of claim 1, wherein the transmissionsystem is of the ultrasound type.
 20. A system of claim 1, wherein thetransmission system uses a continuous monodirectional stream protocol.21. A system of claim 1, wherein the transmission system uses a datagrampackets protocol.
 22. A system of claim 1, wherein the transmissionsystem uses a negotiated asynchronous transport protocol.
 23. A systemof claim 1, wherein the system comprises pre-processing means adapted toperform a pre-processing of all or part of said first pieces ofinformation on board of said wing airfoil to provide pre-processed firstpieces of information.
 24. A system of claim 1, wherein the systemcomprises at least one supplying system of the first detecting means andof the transmission system on board of the wing airfoil.
 25. A system ofclaim 24, wherein the supplying system comprises photovoltaic thin-filmmodules on a plastic support applied on the wing airfoil.
 26. A systemof claim 24, wherein the supplying system comprises an Aeolianmicro-turbine keyed-in on a permanent magnet generator.
 27. A processfor automatically controlling the flight of at least one power wingairfoil, through a system of claim 1, the process comprising the stepsof: a) detecting the first pieces of information through the firstdetecting means related to a current instant of a flight trajectory ofthe wing airfoil; b) detecting the second pieces of information throughthe second detecting means related to a current instant of a flighttrajectory of the wing airfoil c) sending through the transmissionsystem the first pieces of information to the processing and controllingmeans; d) sending the second pieces of information to the processing andcontrolling means; e) from the first and second pieces of informationdirectly or indirectly obtaining values related at least to one currentposition XY and one current flight height of the wing airfoil, to adynamics of the counterweight, and to a traction on the driving cables;f) defining flight and control parameters;— g) defining a relativeweight P_(Q), Pc, P_(M), P_(ZI) P_(T), for each one of the flight andcontrol parameters; h) computing, for each one of the parameters, thebest coordinates XY in following times T₀, T₁, T₂, . . . , T_(n); i)computing a vectorial sum RX₀Y₀ of all coordinates at the time T₀; j)computing the vectorial sums RX₁Y₁, RX₂Y₂, . . . , RX_(n)Y_(n) for allfuture times T₁, T₂, . . . , T_(n); k) defining and applying timeweights PT₀, PT₁, PT₂, . . . , PTn for the vectorial sums; l) choosing abest one among the vectorial sums RX₁Y₁, RX₂Y₂, . . . , RX_(n)Y_(n) asideal instantaneous coordinate (or target) to which a maneuver of thewing airfoil tends; m) choosing a best path of a flight trajectory TV₁,TV₂, TV₃, . . . , TVn, to take the wing airfoil from the currentposition to the target; n) taking the wing airfoil from the coordinateof the current position to the target by acting on the driving unitthrough the numeric control; o) repeating the steps a) to n) at everytime interval Δt.
 28. The process of claim 27, the process comprising,between step a) and step b), the step of re-processing all or part ofthe first pieces of information through the pre-processing means inorder to obtain pre-processed first pieces of information.
 29. Theprocess of claim 27, wherein the flight and control parameters areheight Q, dynamics of the counterweight C, maneuver M, interdictionareas ZI, traction T of the driving cables.
 30. The process of claim 27,wherein the step f) comprises the step of defining a tolerance for eachone of the parameters.
 31. The process of claim 27, wherein the step m)uses an Inertial Navigation System (INS) supported by a dynamic model ofthe wing airfoil (FVM).
 32. The process of claim 27, the processcomprising an emergency step to point out to the wing airfoil whichmaneuver must be performed with maximum priority.
 33. The process ofclaim 27, the process comprising the step of retroactively correctingthe flight and control parameters.
 34. The process of claim 27, theprocess comprising the step of calibrating manoeuvre the maneuverthrough Hinf techniques or Kalman filters.
 35. The process of claim 27,the process comprising the step of retroactively adjusting a length ofthe time interval Δt.
 36. Use of the system of claim 1 together with acarousel-type system.
 37. Use of the process of claim 27 together with acarousel-type system.